1. Field of the Invention
This invention relates to a method for accurately determining the presence or absence of water in low concentration levels in organic fluids and an indicator system which can be employed in this method. More particularly this invention relates to a method for determining the presence or absence of water in non-polar organic fluids such as petroleum oil or hydrocarbon oils which can be performed rapidly without costly instrumentation and tedious and time consuming analytical methods.
2. Description of the Relevant Art
Determination of the presence or absence of water in various organic fluids is quite important. In materials such as transmission fluid, the presence of water at elevated levels has been found to have deleterious affects on mechanical devices using organic fluids such as transmission brake devices, hydraulic devices, etc. Strict tolerances about the absence of water in organic fluids can be seen in other areas as hydraulic oils and petroleum fuel.
Because of this, variety of analytical methods have been developed to determine the water content in organic materials. The classic method for the determination of water is the Karl Fischer method. This method relies on the stoichiometric reaction of water with Karl Fisher reagent, a mixture of pyridine, iodine, sulphur dioxide and methanol. Addition of Karl Fischer reagent to a sample containing water will result in a color change from light yellow in the presence of excess water, to dark brown in the presence of excess Karl Fischer reagent signifying a drop in electrical resistance as the water reacts with reagent. Titration to a specific consistent electro-resistive end point can be used to calculate the water content of a given organic material.
The Karl Fischer method is an accepted and accurate method for water content determination. However, it does have drawbacks. First, the method is time consuming and requires a degree of skill and training to provide accurate results. The apparatus is complex; requiring a meter electrode, numerous drying tubes, agitation means, etc. which must be air-tight in order to function accurately. Second, the method is unable to provide a high degree of accuracy for samples containing smaller amounts of water or various alcohols. Water concentration as low as 0.04% is extremely difficult to accurately detect. However, water level in a given sample below the accurate detection limits of the method can still be sufficient to create problems in the given application. Third, the Karl Fischer reagent, at the least is, unpleasant to work with. The reagent has a relatively short shelf life and can be expensive if large quantities are required. Finally, the reddish brown color of the reagent makes it extremely difficult to titrate red and brown colored samples accurately.
Numerous attempts have been made to modify the Karl Fischer reagent to produce a more cost effective reagent which would yield accurate results at lower water concentrations. These attempts have not produced a quick and reliable method which can be used easily to analyze water content in a variety of fluids or in a field test environment.
A second water determination method which is widely used is the Standard Test Method for Water in Petroleum Products and Bituminous Materials by Distillation (ASTM D 95-70) which is herein incorporated by reference. The material to be tested is heated under reflux with a water immiscible solvent which co-distills with the water in the sample. Condensed solvent and water are continuously separated in a trap with the water settling in a graduated section of the trap while the solvent is returned to the still.
The distillation method is effective for samples containing concentrations of water above approximately 0.5 to 1%. The accuracy decreases as the concentration of water decreases. Thus, the method is not desirable for trace analysis. Distillation by this method is an extremely slow procedure. Accurate determination can take up to an hour or more per sample. This is impractical where large number of samples must be run or there is extreme urgency, as is the case in many situations. As with the Karl Fischer method, supervision of test method by technically trained personnel is highly desirable to maintain accuracy and reproducability.
Other methods such as infrared spectroscopy (IR) and ultracentrafugation are used in certain circumstances. Infrared spectroscopy requires expensive instrumentation operated by experienced analysts as well as careful sample preparation and the use of special IR cells. Ultracentrafugation is not a reliable method for determining water content in highly emulsified samples.
Thus, there has been a great need to develop rapid, accurate, easy, cost-effective method for determining water content in non-polar materials. Despite this ease, accuracy, speed and economy have been elusive goals.
A variety of field test methods for determining the presence of water in organic fluids have been proposed. These methods and devices have resulted in some simplification. However, the methods still have drawbacks.
U.S. Pat. No. 4,577,978 to Pullen et al, discloses a field method for determining small amounts of water in industrial and lubricating oils. A measured amount of test oil is heated in a first self-contained compartment simultaneously with the heating of a reference oil containing a known quantity of water in a second compartment. The operator observes the bubbles generated upon heating to provide a relative indication of the water content in the sample. The test takes about five minutes, but provides only transient evidence of water content. Great reliance must be placed on the operator's power of observation, skill, and reliability. Additionally, this method would not be as effective for oils containing low boiling components.
An aircraft fuel contaminant test unit is discussed in U.S. Pat. No. 3,976,572 to Reick. The device has two chambers connected by a selectively permeable hydrophobic material constructed from non-woven spunbonded polyester or polyethylene fibers. The polymeric fibers are coated with a hydrophobic material which includes fumed silicon dioxide particles. This visual testing device would be effective for gross quantities of water but is not designed for detecting trace amounts. Additionally, the device would be difficult to use successfully to test highly viscous materials. A method for determining the presence minute traces of water in organic liquids was proposed in U.S. Pat. No. 2,950,958 to Nesh. The organic liquid to be tested is mixed with anhydrous carbon tetrachloride and agitated to extract the water molecules from solution. Powdered methylene blue is added to the agitated mixture. Any water released from the liquid material will dissolve the methylene blue triggering a color change.
The drawbacks to the Nesh method are numerous. First, the multi step system in which indicator is added after extraction is cumbersome, time-consuming, and inaccurate. Second, the use of carbon tetrachloride is considered to be unsafe. Third, it is doubtful that the detection levels obtainable by the Nesh method are as sensitive as would be desirable. This may be the reason this method has failed to attain wide acceptance. Finally, it is not believed that this method would be completely effective on pigmented or colored samples.
Thus, it would be desirable to provide a method for detecting water in non-polar materials which is rapid, precise, easy to use, and cost effective and which eliminates the need for complex instrumentation and sample preparation by highly skilled personnel.
It is also desirable to provide an indicator system which can be used to detect the presence of varying amounts of water in a variety of opaque, pigmented or clear liquid samples.
Finally, it is desirable to provide a method and an indicator system which can be used by individuals with little or no technical training and still achieve accurate results.